3 Omitting Files in Dired

Omitting a file means removing it from the directory listing. Omitting
is useful for keeping Dired buffers free of “uninteresting” files (for
instance, auto-save, auxiliary, backup, and revision control files) so that
the user can concentrate on the interesting files. Like hidden files, omitted
files are never seen by Dired. Omitting differs from hiding in several
respects:

Omitting works on individual files, not on directories; an entire directory
cannot be omitted (though each of its files could be).

Omitting is wholesale; if omitting is turned on for a Dired buffer, then all
uninteresting files listed in that buffer are omitted. The user does not omit
(or unomit) files one at a time.

Omitting can be automatic; uninteresting file lines in the buffer can be
removed before the user ever sees them.